Beauveria Species

Taxonomic Classification

Description and Natural Habitats

This hyaline, filamentous fungus first recognized as the etiologic agent of the devastating muscardine disease of the silkworm, is ubiquitous in plant debris and soil. Beauveria is also isolated from foodstuff, infected insects, and indoor air environment.

Species

The genus Beauveria contains several species. The most common ones are Beauveria bassiana and Beauveria alba.

Pathogenicity and Clinical Significance

Beauveria bassiana is a very rare human pathogen. It may be associated with keratitis. Pneumonia in an immunocompromised patient due to Beauveria has also been reported. As noted previously, it is well-known to cause infections in insects and some other animals.

Macroscopic Features

The growth rate of Beauveria is moderately rapid. The colonies reach a diameter of 1 to 3 cm following incubation at 25°C for 7 days on potato glucose agar. The texture is cottony to powdery or mealy. The surface is white to yellowish white or pale pinkish in color. The reverse is white or pale [462, 1295, 2144].

Microscopic Features

The hyphae are hyaline, septate, and narrow. The conidiogenous cells on the hyphae are typically flask-shaped with an inflation at the base and narrow zigzagging filaments at the apex. Laterally from the filament, conidia are produced from each bending point. This type of conidium production is called sympodial geniculate growth. The conidia (diameter: 2-4 µm) are hyaline, one-celled and globose to ovoid in shape. The conidiogenous cells tend to form dense clusters. These clusters appear as small powdery balls in the aerial hyphae when viewed through dissecting microscope. Since the cluster formation makes it difficult to visualize the arrangement and structure of conidia, examination of young cultures is optimal for detailed microscopic view [462, 1295, 2144].

Histopathologic Features

Hyaline, septate hyphae (2-8 µm wide) are observed. The contours of the hyphae are regular and branches are random.